Our major aim is to understand the changes in nuclei of aneuploid CNS neoplasms. Isolation and characterization of subsets of repeated sequences in mouse and human DNA will be continued, with emphasis on chromosomal structure (studied by in situ hybridization) and DNA analysis. Ultrastructural studies of the nucleolus organizing regions in interphase nuclei will be correlated with quantitative analysis of DNA restriction profiles from normal and neuroectodermal tumor cells using defined ribosomal DNA probes. Methods to analyze ribosomal and other DNA sequence subsets of interest, with respect to their sequence, distribution, and three-dimensional arrangement in chromosomes and interphase nuclei, are being pursued. Recent progress with biotin-labeled DNA probes has allowed high-resolution (EM) studies of specific DNA sequences in preparations of interphase and metaphase chromosomes. These studies indicate specific three-dimensional arrangements of selected DNA sequences in differentiated CNS cell types and significant alterations in CNS tumor cells. (I)